Light-emitting element having a reflective structure with high efficiency

ABSTRACT

An optoelectronic element comprises a semiconductor stack comprising an active layer, wherein the semiconductor stack has a first surface and a second surface opposite to the first surface; a first transparent layer on the second surface; a plurality of cavities in the first transparent layer; and a layer on the first transparent layer, wherein the first transparent layer comprises oxide or diamond-like carbon.

REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 14/286,685, filed on May, 23, 2014, which claimsthe right of priority based on TW application Serial No. 102118593,filed on May 24, 2013, and the content of which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

The application relates to a light emitting element, and moreparticularly to a light emitting element having a reflective structurewith high efficiency.

DESCRIPTION OF BACKGROUND ART

An optoelectronic element, such as a light-emitting diode (LED), hasbeen applied widely to optical display devices, traffic signals, datastoring devices, communication devices, illumination devices, andmedical apparatuses. Besides, the LED can be connected with otherelements to form a light-emitting apparatus. FIG. 1 illustrates aschematic view of a conventional light-emitting apparatus. As shown inFIG. 1, a conventional light-emitting apparatus 1 includes a submount 12with a circuit 14; a solder 16 on the submount 12, wherein an LED 11 isadhesively fixed on the submount 12 by the solder 16; and an electricalconnecting structure 18 is electrically connecting the electrode 15 andthe circuit 14 on the submount 12. Wherein, the submount 12 can be alead frame or a mounting substrate.

SUMMARY OF THE DISCLOSURE

An optoelectronic element comprises a semiconductor stack comprising anactive layer, wherein the semiconductor stack has a first surface and asecond surface opposite to the first surface; a first transparent layeron the second surface; a plurality of cavities in the first transparentlayer; and a layer on the first transparent layer, wherein the firsttransparent layer comprises oxide or diamond-like carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of a conventional light-emitting apparatus.

FIG. 2 shows an illustration of a cross section of a light-emittingelement in accordance with one embodiment of the present application.

FIG. 3 shows an illustration of a cross section of a light-emittingelement in accordance with another embodiment of the presentapplication.

FIG. 4 shows an illustration of the deposition direction of the secondtransparent layer in accordance with the embodiment shown in FIG. 3.

FIG. 5 shows an illustration of a cross section of a light-emittingelement in accordance with another embodiment of the presentapplication.

FIG. 6 shows an illustration of the explosion of a light bulb inaccordance with one embodiment of the present application.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiments of the present application are described in detail andpresented in the drawings. The same or similar parts are indicated withthe same numbers in the drawings and the specification.

FIG. 2 shows a cross section of a light-emitting element in accordancewith one embodiment of the present application. As shown in FIG. 2, thelight-emitting element 2 includes a substrate 20, an adhesive layer 22being disposed on the substrate 20, a reflective structure 24 beingdisposed on the adhesive layer 22, a light-emitting stack 26 beingdisposed on the reflective structure 24, a first electrode 21 beingdisposed under the substrate 20, and a second electrode 23 beingdisposed on the light-emitting stack 26. The light-emitting stack 26includes a first semiconductor layer 262 being disposed on thereflective structure 24, an active layer 264 being disposed on the firstsemiconductor layer 262, and a second semiconductor layer 266 beingdisposed on the active layer 264.

The first electrode 21 and/or the second electrode 23 can receive theexternal voltage and can be composed of the transparent conductivematerial or the metal material. The transparent conductive materialincludes but is not limited to Indium-Tin Oxide (ITO), Indium Oxide(InO), Tin Oxide (SnO), Cadmium Tin Oxide (CTO), Antimony Tin Oxide(ATO), Aluminum Zinc Oxide (AZO), Zinc Tin Oxide (ZTO), Gallium ZincOxide (GZO), Zinc Oxide (ZnO), Gallium Phosphide (GaP), Indium ZincOxide (IZO), Diamond-like Carbon (DLC), Indium Gallium Oxide (IGO),Gallium Aluminum Zinc Oxide (GAZO), or the combination thereof. Themetal material includes but is not limited to Aluminum (Al), Chromium(Cr), Copper (Cu), Tin (Sn), Gold (Au), Nickel (Ni), Titanium (Ti),Platinum (Pt), Lead (Pb), Zinc (Zn), Cadmium (Cd), Antimony (Sb), Cobalt(Co), or the alloy thereof.

The light-emitting stack 26 includes a rough upper surface 261 and arough lower surface 263 to reduce the probability of internal totalreflection and to enhance the light extraction efficiency. The roughupper surface includes a flat portion 265 which the second electrode 23could be disposed thereon to enhance the adhesion between the secondelectrode 23 and the light-emitting stack 26 and to reduce theprobability the second electrode 23 peeling off from the light-emittingstack 26 due to the sequential manufacturing processes such as wirebonding. The material of the light-emitting stack 26 could be asemiconductor material including more than one element such as Gallium(Ga), Aluminum (Al), Indium (In), Phosphorous (P), Nitrogen (N), Zinc(Zn), Cadimum (Cd), and Selenium (Se). The first semiconductor layer 262and the second semiconductor layer 266 have different polarities and areused to produce electrons and holes. The active layer 264 can emit onesingle color or multiple colors, and the color(s) can be visible orinvisible. The structure of the active can be a hetero-structure, adouble hetero-structure, a double-sided double hetero-structure, amulti-layered multi-quantum-well structure, or a quantum-dot structure.

The reflective structure 24, along the direction from the adhesive layer22 toward the light-emitting stack 26, includes a reflective layer 242,a first transparent layer 244, and a window layer 248. Optionally, asecond transparent layer 246 can be formed additionally. In oneembodiment, only the first transparent layer 244 is presented. In suchembodiment, the window layer 248 includes a rough lower surface, and therouge lower surface includes a plurality of protruding portions 241 andconcave portions 243. Wherein, the rough lower surface further includesa flat portion located right under the second electrode 23 being used toform an ohmic contact with the first transparent layer 244. At least onecavity 245 is formed in the first transparent layer 244 and the cavity245 can be extended from rough lower surface of the window layer 248downward to the reflective layer 242. In another embodiment, the cavity245 can be extended from the protruding portion 241 downward to thereflective layer 242. Wherein, the refractive index of the cavity 245 issmaller than the refractive indices of the window layer 248 and thefirst transparent layer 244. Because the refractive index of the cavity245 is smaller than the refractive indices of the window layer 248 andthe first transparent layer 244, the critical angle at the interfacebetween the window layer 248 and the cavity 245 is smaller than thecritical angle at the interface between the window layer 248 and thefirst transparent layer 244. After the light which is emitted from thelight-emitting stack 26 emitting toward the cavity 245, the probabilityof the total reflection occurred at the interface between the windowlayer 248 and the cavity 245 increases. Besides, if the light at theinterface between the window layer 248 and the cavity 245 not forming atotal reflection and entering the first transparent layer 244, the totalreflection is also occurred at the interface between the firsttransparent layer 244 and the cavity 245 and therefore to enhance thelight extraction efficiency of the light-emitting element 2. Taking aview of the cross section, the cavity 245 is in the shape of a funnelwith a wide upper part and a narrow lower part.

In another embodiment, the reflective structure 24 can further include asecond transparent layer 246 located between part of the firsttransparent layer 244 and the window layer 248 to enhance the adhesionand the spreading of the current between the first transparent layer 244and the window layer 248. In another embodiment, the second transparentlayer 246 can include a cavity 245, and wherein the refractive index ofthe cavity 245 is smaller than the refractive indices of the windowlayer 248 and the second transparent layer 246. Because the refractiveindex of the cavity 245 is smaller than the refractive indices of thewindow layer 248 and the second transparent layer 246, the criticalangle at the surface between the second transparent layer 246 and thecavity 245 is smaller than the critical angle at the surface between thewindow layer 248 and the second transparent layer 246. After the lightwhich is emitted from the light-emitting stack 26 emitting toward thecavity 245, the probability of the total reflection occurred at theinterface between the second transparent layer 246 and the cavity 245increases. In another embodiment, the reflective structure 24 does nothave the window layer 248, and the first transparent layer 244 is formedunder the light-emitting stack 26. In the embodiment, the rough lowersurface 263 of the light-emitting stack 26 includes a plurality ofprotruding portions and concave portions and therefore is favorable offorming the cavity 245.

The window layer 248 is transparent to the light emitted by thelight-emitting stack 26 and is used to enhance the light extractionefficiency. The material of the window layer can be a conductivematerial, which includes but is not limited to Indium-Tin Oxide (ITO),Indium Oxide (InO), Tin Oxide (SnO), Cadmium Tin Oxide (CTO), AntimonyTin Oxide (ATO), Aluminum Zinc Oxide (AZO), Zinc Tin Oxide (ZTO),Gallium Zinc Oxide (GZO), Zinc Oxide (ZnO), Gallium Phosphide (GaP),Indium Zinc Oxide (IZO), Diamond-like Carbon (DLC), Indium Gallium Oxide(IGO), Gallium Aluminum Zinc Oxide (GAZO), or the combination thereof.The height difference h between the concave portion 243 and theprotruding portion 241 of the rough lower surface is about ⅓ to ⅔ thethickness of the window layer and is favorable of forming the cavity245.

The materials of the first transparent layer 244 and/or the secondtransparent layer 246 are transparent to the light emitted by thelight-emitting stack 26 and is used to increase the adhesion and thespreading of the current between the window layer 248 and the reflectivelayer 242. Besides, the materials of the first transparent layer 244and/or the second transparent layer 246 can form an Omni-DirectionalReflector (ODR) with the reflective layer 242. The material of the firsttransparent layer 244 and/or the second transparent layer 246 can be atransparent conductive material which includes but is not limited toIndium-Tin Oxide (ITO), Indium Oxide (InO), Tin Oxide (SnO), Cadmium TinOxide (CTO), Antimony Tin Oxide (ATO), Aluminum Zinc Oxide (AZO), ZincTin Oxide (ZTO), Gallium Zinc Oxide (GZO), Zinc Oxide (ZnO), GalliumPhosphide (GaP), Indium Zinc Oxide (IZO), Diamond-like Carbon (DLC),Indium Gallium Oxide (IGO), Gallium Aluminum Zinc Oxide (GAZO), or thecombination thereof. The method of forming the first transparent layer244 and/or the second transparent layer 246 includes the physical vapourdeposition method, such as E-beam deposition or sputtering. Thereflective layer 242 can reflect the light from the light-emitting stack26 and the material can be a metal material, which includes but is notlimited to Copper (Cu), Aluminum (Al), Tin (Sn), Gold (Au), Silver (Ag),Lead (Pb), Titanium (Ti), Nickel (Ni), Platinum (Pt), Tungsten (W), orthe alloy thereof.

The adhesive layer 22 can connect the substrate 20 and the reflectivestructure 24 and can include a plurality of sublayers (not shown). Thematerial of the adhesive layer 22 can be a transparent conductivematerial or a metal material, the transparent conductive materialincludes but is not limited to Indium-Tin Oxide (ITO), Indium Oxide(InO), Tin Oxide (SnO), Cadmium Tin Oxide (CTO), Antimony Tin Oxide(ATO), Aluminum Zinc Oxide (AZO), Zinc Tin Oxide (ZTO), Gallium ZincOxide (GZO), Zinc Oxide (ZnO), Gallium Phosphide (GaP), Indium CeriumOxide (ICO), Indium Tungsten Oxide (IWO), Indium Titanium Oxide (ITiO),Indium Zinc Oxide (IZO), Indium Gallium Oxide (IGO), Gallium AluminumZinc Oxide (GAZO), or the combination thereof. The metal materialincludes but is not limited to Copper (Cu), Aluminum (Al), Tin (Sn),Gold (Au), Silver (Ag), Lead (Pb), Titanium (Ti), Nickel (Ni), Platinum(Pt), Tungsten (W), or the alloy thereof.

The substrate 20 can be used to support the light-emitting stack 26thereon and other layers or structures, and its material can be atransparent material or a conductive material. The transparent materialcan include but is not limited to Sapphire, Diamond, Glass, Epoxy,Quartz, Acryl, Aluminum Oxide (Al₂O₃), Zinc Oxide (ZnO), or AluminumNitride (AlN) and so on. The conductive material can include but is notlimited to Copper (Cu), Aluminum (Al), Molybdenum (Mo), Tin (Sn), Zinc(Zn), Cadmium (Cd), Nickel (Ni), Cobalt (Co), Diamond Like Carbon (DLC),Graphite, Carbon fiber, Metal Matrix Composite (MMC), Ceramic MatrixComposite (CMC), Silicon (Si),, Zinc Selenium (ZnSe), Gallium Arsenide(GaAs), Silicon Carbide (SiC), Gallium Phosphide (GaP), Gallium ArsenicPhosphide (GaAsP), Lithium Gallium Oxide (LiGaO₂), or Lithium AluminumOxide (LiAlO₂).

FIG. 3 discloses a cross section of a light-emitting element inaccordance of another embodiment of the present application. Alight-emitting element 3 includes a similar structure to theaforementioned light-emitting element 2, but the second transparentlayer 246 of the reflective structure 24 includes a plurality ofcavities 30 so that the refractive index of the second transparent layer246 is smaller than 1.4, and is preferred to be 1.35. As shown in FIG.4, the cavities 30 are formed by fixing the wafer 4 to a specificdirection, such as the direction D which has an included angle θ withthe normal perpendicular to the wafer, to deposit the material of thesecond transparent layer 246 onto the wafer by the physical vapourdeposition method. Because of the adjustment of the deposition directionD, there are some areas that the material is not deposited onto and thecavities are formed. Wherein, the included angle is about 60 degrees.The refractive index of the second transparent layer 246 with cavities30 is smaller than the transparent layer without the cavities, theprobability of the total reflection occurred at the interface betweenthe second transparent layer 246 and another layer can be increased, andtherefore the light extraction efficiency of the light-emitting element3 is enhanced. The first transparent layer 244 can be formed by thephysical vapour deposition method or the chemical vapour depositionmethod under the second transparent layer 246 and has a thickness largerthan that of the second transparent layer 246 so that it can prevent thematerial of the reflective layer 242 from diffusing into the cavitiesand destroying the structure of the reflective layer 242 and decreasethe reflectivity of the reflective layer 242. The first transparentlayer 244 includes a lower surface 247, which can be polished by thechemical mechanical polishing method (CMP) to make it has an averageroughness of the center line (Ra) about 1 nm˜40 nm. When the reflectivelayer 242 is formed under the first lower surface 247, the reflectivelayer 242 can form a surface with a lower average roughness of thecenter line (Ra) and therefore increase the reflectivity of thereflective layer 242.

The light-emitting element 3 further includes a conductive portion 32located between the light-emitting stack 26 and the reflective layer242. In another embodiment, the conductive portion 32 can be locatedbetween the window layer 248 and the reflective layer 242. Theconductive portion 32 can conduct the current. The material of theconductive portion can be a transparent conductive material or a metalmaterial. The transparent conductive material can be but is not limitedto Indium-Tin Oxide (ITO), Indium Oxide (InO), Tin Oxide (SnO), CadmiumTin Oxide (CTO), Antimony Tin Oxide (ATO), Aluminum Zinc Oxide (AZO),Zinc Tin Oxide (ZTO), Gallium Zinc Oxide (GZO), Zinc Oxide (ZnO),Gallium Phosphide (GaP), Indium Cerium Oxide (ICO), Indium TungstenOxide (IWO), Indium Titanium Oxide (ITiO), Indium Zinc Oxide (IZO),Indium Gallium Oxide (IGO), Gallium Aluminum Zinc Oxide (GAZO), or thecombination thereof. The metal material includes but is not limited toCopper (Cu), Aluminum (Al), Tin (Sn), Gold (Au), Silver (Ag), Lead (Pb),Titanium (Ti), Nickel (Ni), Platinum (Pt), Tungsten (W), Germanium (Ge),or the alloy thereof.

In this embodiment, the material of the first transparent layer 244and/or the second transparent layer 246 can be an insulating materialsuch as Polyimide (PI), Benzocyclobutene (BCB), Perfluorocyclobutane(PFCB), Magnesium oxide (MgO), SU8, Epoxy, Acrylic resin, CycloalkenesCopolymer (COC), Poly(methyl methacrylate) (PMMA), Poly (ethyleneterephthalate) (PET), Polycarbonate (PC), Polyetherimide, Fluorocarbonpolymer, Glass, Aluminum Oxide (Al₂O₃), Silicon Oxide (SiOx), TitaniumOxide (TiO₂), Tantalic Oxide (Ta₂O₅), Silicon Nitride (SiNx), MagnesiumFluoride (MgF₂), Spin-on-glass (SOG), or Tetraethyl orthosilicate(TEOS).

FIG. 5 discloses a cross section of a light-emitting element inaccordance of another embodiment of the present application. As shown inFIG. 5, a light-emitting element 5 includes a substrate 50; alight-emitting stack 52 on the substrate 50; a reflective structure 54on the light-emitting stack 52; and an electrode 56 on the reflectivestructure 54. The light-emitting stack 52 includes a first semiconductorlayer 522 located on the substrate 50; an active layer 524 located onthe first semiconductor layer 522; and a second semiconductor layer 526located on the active layer 524. Wherein, a portion of the semiconductorlayer 526 and the active layer 524 are removed in order to expose thefirst semiconductor layer 522.

The reflective structure 54 includes a window layer 540 located on thelight-emitting stack 52; a first transparent layer 542 located on thewindow layer 540; a reflective layer 544 located on the firsttransparent layer 542; and a first insulating layer 546 located on thereflective layer 544. The window layer 540 includes a rouge uppersurface 541, and the rouge upper surface includes a plurality ofprotruding portions 543 and concave portions 545. At least one cavity547 is formed in the first transparent layer 542 and on the rough uppersurface 541. The refractive index of the cavity 547 is smaller than therefractive indices of the window layer 540 and of the first transparentlayer 542. In another embodiment, the cavities 547 can be extendedupward from the concave portions 545. Because the refractive index ofthe cavities 547 is smaller than the refractive indices of the windowlayer 540 and the first transparent layer 542, the critical angle at theinterface between the window layer 540 and the cavities 547 is smallerthan the critical angle at the interface between the window layer 540and the first transparent layer 542. After the light which is emittedfrom the light-emitting stack 52 emitting toward the cavity 547, theprobability the total reflection occurred at the interface between thewindow layer 540 and the cavity 547 increases. Besides, the light notforming a total reflection at the interface between the window layer 540and the first transparent layer 542 enters the first transparent layer542 and the total reflection is occurred at the interface between thefirst transparent layer 542 and the cavity 547 and therefore to enhancethe light extraction efficiency of the light-emitting element 5. Viewingfrom the cross section, the cavity 547 is in the shape of a funnel witha wide upper part and a narrow lower part. Because the probability ofthe total reflection occurred for the light emitted from thelight-emitting stack 52 at the interface between the window layer 540and the cavities 547 and at the interface between the first transparentlayer 542 and the cavities 547 increases, the probability the lightarrives to the electrode 56 and is absorbed by the electrode 56 isdecreased, and the light extraction efficiency of the light-emittingelement 5 is increased. The first insulating layer 546 can cover thereflective layer 544 so that the reflective layer 544 does not directlycontact with the electrode 56 in order to prevent the material of thereflective layer 544 from diffusing to the electrode 56 and decreasingthe reflectivity of the reflective layer 544. The reflective structure54 further includes a plurality of channels 549 formed in the firsttransparent layer 542 and in the first insulating layer 546 so that theelectrode 56 can electrically contact with the light-emitting stack 52through the channels 549. The reflective structure 54 can furtherinclude a second transparent layer 548 located between part of the firsttransparent layer 542 and the reflective layer 544. The secondtransparent layer 548 does not include the cavities so that it canprevent the material of the reflective layer 544 from diffusing to thecavities and destroying the structure of the reflective structure 544,which degrades the reflectivity of the reflective layer 544.

The electrode 56 includes a first conductive layer 562 and a secondconductive layer 564, and wherein the first conductive layer 562 and thesecond conductive layer 564 does not contact each other. The firstconductive layer 562 connects the first semiconductor layer 522 throughthe channels 549, and the second conductive layer 564 connects thewindow layer 540 through the channels 549. In another embodiment, thelight-emitting element 5 further includes a first contact layer 51located between the first conductive layer 562 and the firstsemiconductor layer 522 in order to increase the adhesion between thefirst conductive layer 562 and the first semiconductor layer 522. Thesecond contact layer 53 is located between the second conductive layer564 and the window layer 540 in order to increase the adhesion betweenthe second conductive layer 564 and the window layer 540, to decreasethe operating voltage of the light-emitting element 5, and to increasethe efficiency. Wherein, the materials of the first contact layer 51 andthe second contact layer 52 is the same as the materials of theaforementioned electrodes.

FIG. 6 discloses an illustration of the explosion of a light bulb. Alight bulb 6 includes a globe 61, a lens 62 located in the globe 61, alight-emitting module 64 located under the lens 62, a lampstand 65including a heat dissipation tank 66 used to support the light-emittingmodule 64, a connecting portion 67, and an electrical connectingapparatus 68. Wherein, the connecting portion 67 connects the lampstand65 and the electrical connecting apparatus 68. The light-emitting module66 includes a supporting body 63 and a plurality of the light-emittingelements 60 in accordance with any one of the aforementioned embodimentlocated on the supporting body 63.

Although the present application has been explained above, it is not thelimitation of the range, the sequence in practice, the material inpractice, or the method in practice. Any modification or decoration forpresent application is not detached from the spirit and the range ofsuch.

What is claimed is:
 1. An optoelectronic element, comprising: asemiconductor stack comprising an active layer, wherein thesemiconductor stack has a first surface and a second surface opposite tothe first surface; a first transparent layer on the second surface; aplurality of cavities in the first transparent layer; and a layer on thefirst transparent layer; wherein the first transparent layer comprisesoxide or diamond-like carbon.
 2. The optoelectronic element according toclaim 1, wherein the second surface comprises a second rough portion anda second flat portion, and one of the cavities is on the second roughportion.
 3. The optoelectronic element according to claim 2, furthercomprising an electrode on the first surface, wherein the second flatportion is right under the electrode.
 4. The optoelectronic elementaccording to claim 2, wherein the second flat portion and the firsttransparent layer form an ohmic contact.
 5. The optoelectronic elementaccording to claim 2, wherein the first surface comprises a first flatportion and a first rough portion, and the electrode is on the firstflat portion.
 6. The optoelectronic element according to claim 1,wherein a refractive index of the cavity is smaller than that of thefirst transparent layer and the semiconductor stack.
 7. Theoptoelectronic element according to claim 1, wherein the layer comprisesa surface facing the semiconductor stack, and the surface has an averageroughness of the center line between 1 nm and 40 nm.
 8. Theoptoelectronic element according to claim 1, further comprising a secondtransparent layer between the first transparent layer and the layer. 9.The optoelectronic element according to claim 8, wherein the secondtransparent layer has a thickness larger than that of the firsttransparent layer.
 10. The optoelectronic element according to claim 1,wherein the layer comprises a material selected from Copper (Cu),Aluminum (Al), Gold (Au), Silver (Ag) or the alloy thereof.
 11. Theoptoelectronic element according to claim 1, wherein the semiconductorstack comprises a window layer.
 12. The optoelectronic element accordingto claim 11, wherein the window layer comprises GaP.
 13. Theoptoelectronic element according to claim 1, further comprising asubstrate on the layer, and an adhesive layer between the substrate andthe layer for connecting thereof.
 14. The optoelectronic elementaccording to claim 1, wherein the first transparent layer comprises aplurality of channels.
 15. The optoelectronic element according to claim14, further comprising a first conductive layer and a second conductivelayer on the layer, wherein the first conductive layer and the secondconductive layer are separated.
 16. The optoelectronic element accordingto claim 15, wherein the first conductive layer electrically contactingwith the semiconductor stack through the plurality of channels.
 17. Theoptoelectronic element according to claim 15, wherein the layercomprises a reflective layer.
 18. The optoelectronic element accordingto claim 17, further comprising a second transparent layer between thelayer and the first conductive layer.
 19. The optoelectronic elementaccording to claim 1, wherein one of the cavities has an opening facingthe second surface.
 20. The optoelectronic element according to claim 1,wherein the layer covers one of the cavities.